Low body weight and cardiac tolerance to ischemia in neonatal rats.

Adaptation to intermittent high altitude hypoxia (IHAH) increases tolerance of the isolated neonatal rat heart to ischemia and potentiates protection induced by ischemic preconditioning. In addition to the protective effect, IHAH significantly reduces growth of the animals. The aim of the present study was, therefore, to find out whether low body weight per se might influence cardiac sensitivity to oxygen deprivation. Low body weight was induced either by IHAH (barochamber, 8 h/day, 5000 m) from postnatal day 1 to 10 (HLBW), or by a higher number of sucklings per mother (14 instead of 8), again from postnatal day 1 to 10 (NLBW). Control animals (8 littermates per mother) were kept under normoxic conditions (Controls). The recovery of developed force following 40 min of global ischemia was measured in isolated hearts from 10-day-old rats by perfusing them in the Langendorff mode with Krebs-Henseleit solution at constant pressure, temperature and rate. Ischemic preconditioning was induced by three 3-min periods of global ischemia, each separated by 5-min periods of reperfusion. Low body weight in HLBW and NLBW groups was accompanied by increased hematocrit, and decrease in absolute heart weight (both wet and dry) and developed force. On the other hand, higher hydration, increased cardiac tolerance to ischemia and potentiation of protection by ischemic preconditioning were observed in HLBW rats only. This experimental group also exhibited the highest relative heart weight. It may be concluded that low body weight alone does not influence cardiac tolerance to ischemia in neonatal rats.